The present technique relates to superconducting magnet systems and, more particularly, to systems for handling such superconducting magnets, particularly during transportation, servicing, and installation.
A number of important applications exist for superconductive magnet systems. These include imaging systems, as for medical imaging, as well as spectrometry systems, typically used in materials analysis and scientific research applications. The present technique relates to management of cryogenically cooled superconductive magnets, and particularly to the servicing of such systems. Although reference is made throughout the following discussion to imaging systems, it should be borne in mind that the technique is applicable to a range of systems that utilize cryogenically cooled superconducting magnets.
Imaging devices are omnipresent in typical medical environments. Medical practitioners, such as physicians, may employ medical imaging devices to diagnose patients. Imaging devices, such as Magnet Resonance Imaging (MRI) devices and Nuclear Magnetic Resonance (NMR) devices, produce detailed images of a patient's internal tissues and organs, thereby mitigating the need for invasive exploratory procedures and providing valuable tools for identifying and diagnosing disease and for verifying wellness.
Typical MRI and NMR devices develop diagnostic images by affecting gyro-magnetic materials within a patient via controlled gradient magnetic fields and radiofrequency pulses in the presence of a main magnetic field developed by a superconductive magnet. During an MRI exam, a main magnetic field of upwards of two Tesla may be necessary to produce vivid images. Typically, superconductive electromagnets comprise loops of coiled wire, which are continuously bathed in a cryogen, such as liquid helium, at temperatures near absolute zero—approximately at −4K or −271C. When cooled to such extreme temperatures, the coiled wire becomes superconductive, i.e., the electrical resistance of the wire falls to essentially zero, enhancing the field strength without requiring significant energy input for continued operation. Advantageously, superconductive electromagnets reduce the electrical load requirements for producing the desired magnetic fields, thereby making the MRI system more economical to operate.
Cryogenic liquids, such as liquid helium, however, are relatively expensive to produce and maintain. Moreover, because of its low boiling point, liquid helium is a volatile liquid that transitions into a gaseous phase at relatively low temperatures. Accordingly, to conserve helium, typical MRI devices include a cryogen cooling system, which recondenses volatilized helium back into its liquid phase. That is, the helium is maintained in a sealed helium vessel that provides gaseous helium to the cooling system and receives liquid helium from the cooling system in a closed loop process.
However, from time to time, the cryogen cooling system may require maintenance and/or replacement. For example, the performance of the cooling system components may degrade, thereby reducing the efficacy of the cooling system. Moreover, leaks within the helium vessel and/or cooling system, again for example, may also reduce the efficacy of the cooling system. During maintenance, it may become necessary to disengage the cooling system and/or deactivate the MRI devices, events that are to be avoided. If the cooling system is off-line or not cooling effectively, more of the liquid helium may begin to volatilize, leading to an increase of pressure in the helium vessel. To prevent adverse effects due to the increased pressure, traditional MRI devices may relieve pressure by venting some of the gaseous helium to the atmosphere. The conversion of liquid helium to its gaseous state is generally known in the industry as “boil-off,” and, venting of the gas leads to permanent loss expensive cryogen, requiring periodic refilling of the system.
To at least partially remedy these drawbacks of traditional systems, approaches have been developed for cooling superconductive magnets that are sometimes referred to as “zero boil-off” systems. In such systems a refrigeration system or “cold head” essentially runs continuously to recondense vaporized cryogen. An electric heater in the vessel then heats the cryogen to maintain a desired pressure level, thereby preventing the vessel pressure from falling below a desired level that could result in drawing atmospheric gases into the vessel. A balance is maintained between cooling and heating components that can be continuously monitored.
Traditionally, the maintenance of cooling systems in MRI devices is a reactive process. That is, technicians are generally called when, for example, image quality has been affected, a critical indicator has activated, and/or the system is no longer operable. For example, a typical system may generate a service call when a low level of cryogen is detected due to venting or leaks in the system. In addressing concerns reactively, the repair time and/or off-line periods may be longer than desired. For example, certain parts and/or technicians may not be immediately available, leading to longer than necessary downtimes (i.e., off-line time). Moreover, periods of reactive maintenance may not coincide with already scheduled routine maintenance procedures, leading to duplicative downtimes for the MRI device. Similarly, when substantial quantities of cryogen are required, very significant costs may be incurred in refilling the serviced system.
Similar problems exist even prior to the time such magnets are placed in operation. For example, magnets are typically built and tested in a controlled factory environment, then at least partially disassembled from other support equipment for shipping. Current procedures for building, testing and shipping superconductive magnets do not, however, adequately accommodate boil-off or servicing needs. In much the same way, mobile MRI systems and systems where communications infrastructures are less available pose particular challenges beyond those of traditional fixed locations in hospitals. Such challenges include cryogen monitoring and servicing, but also location and identification of the systems, and communication of relevant parameter data to a monitoring or service-coordinating location.
Accordingly, there is a need for an improved technique for transporting cryogen cooling systems. Particularly, there is a need for a technique that reduces the adverse effects of transportation of superconducting magnets and cryogenic cooling systems.